1. Field of the Invention
The present invention relates to an adhesive and, more particularly,to an adhesive which can suitably be used in bonding parts of various devices such as optical devices, liquid crystal display devices, fluid devices, ink jet heads, and other finely processed parts.
2. Related Background Art
Hitherto, adhesives of acryl-type, polythiol-type and polyene-type have been used for the purpose of bonding optical parts, because of their advantages such as high transparency, low viscosity without the aid of any solvent, and high cure speed by irradiation with ultraviolet rays.
Bonding of parts of a liquid crystal display device employs an adhesive which is applied in a predetermined pattern by printing or by transfer from a transfer sheet. Epoxy-type adhesives are usually used in this field.
These known adhesives generally exhibit high fluidity at normal temperatures so that they tend to flow and spread to regions where the application of adhesive is not necessary. This tendency is quite undesirable in bonding finely processed parts such as parts of an ink jet head or a liquid crystal display device, and adversely affects the quality of the products. In the production of an ink jet recording head,for example, a pair of plates having finely processed protrusions and recesses as shown in FIGS. 1(a) and 1(b) are bonded together at their protrusions by means of an adhesive 3 so as to form fine liquid channels 4. If the adhesive 3 spreads into the fine liquid channels 4, the ink discharge characteristics of such channels 4 are undesirably changed. In the worst case, the fine liquid channel 4 may be completely blocked by the adhesive 3 with the result that the ink jet recording head cannot operate at all. In the case of a liquid crystal display device, a spread of an adhesive to an area where bonding is not necessary may impair the display function or, in the worst case, completely disables the display.
On the other hand, adhesives have been proposed and used which have minimum fluidity and, hence, exhibit a minimal tendency of flowing or spreading. Examples of such adhesives are: hot melts to vinyl chloride-type or vinyl acetate-type, B-staged epoxy resin film,and adhesive films of thermoplastic polyester, polyamide and polyimide. These adhesives or adhesive film are used under application of heat by a local heating method. Since the bonding can be finished in quite a short time, and since the fluidity is very low, these adhesives or adhesive films are suitably used in bonding parts of ink jet recording heads or liquid crystal display devices. As mentioned above, these adhesives or adhesive films are used under application of heat produced by a local heating which is typically supersonic heating or microwave heating. In general, however, the mounting of parts to be bonded on the local heating apparatus encounters various restrictions. In addition, such local heating apparatus are expensive. It should also be pointed out that the adhesive film can be used only in bonding flat surfaces.
In the case of the production of a liquid crystal display device, the adhesive is applied in a predetermined pattern by printing or by transfer from a transfer sheet. There is a practical limit in the precision of positional alignment of the pattern. In addition, the resolution of the pattern also has a practical limit of 0.2 mm or so. Thus, this bonding method cannot be employed when higher bonding precision is required.